Microfabricated device

ABSTRACT

A microfabricated device ( 10 ) includes a structure ( 12 ) defining a closed fluid delivery channel ( 14 ), the channel ( 14 ) having an inlet ( 16 ) and an opposed outlet ( 18 ). A conducting polymer actuator ( 20 ) is arranged within the fluid delivery channel ( 14 ). At least a part of the actuator ( 20 ) is configured to vary its cross sectional area in a direction transverse to a direction of fluid flow in the channel ( 14 ). An actuator control arrangement ( 22 ) is carried by the structure ( 12 ) for controlling the actuator ( 20 ) to cause the actuator ( 20 ) to expand and contract cyclically and sequentially along the length of the actuator ( 20 ) to vary the cross sectional area of the channel ( 14 ) cyclically and sequentially to effect a peristaltic pumping action to deliver fluid from the inlet ( 16 ) of the channel ( 14 ) to the outlet ( 18 ) of the channel ( 14 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Australian ProvisionalPatent Application No 2005904179 filed on 4 Aug. 2005, the contents ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a microfabricated device. The inventionrelates particularly, but not necessarily exclusively, to amicrofabricated pumping device. The microfabricated pumping device shallbe referred to below as a “micropump”.

BACKGROUND OF THE INVENTION

The use of microfabricated devices for various applications is becomingincreasingly prevalent. Such devices have found applications as pumpsfor controlled release of drugs into a patient's body, as well asapplications with microchips for microfluidics and analytics.

To provide control of the device, electrical devices are preferred and,generally, electrically powered pumps make use of actuators requiringvoltages of the order of 10-100 volts such as, for example,piezoelectric actuators. Therefore, the devices need to be made ofmaterials having a dielectric strength which can withstand suchvoltages. This increases the bulk of the devices. Further, such devicesmay not be biocompatible and the voltage required does not make themsuitable for implantation. Still further, the response time of suchdevices can, in certain circumstances, be inadequate.

Also, such pumps do not sufficiently accurately meter fluids in themicrolitre, nanolitre or picolitre ranges which may be required foranalytical purposes, medical purposes or other purposes. A number ofthese pumps are also only operable unidirectionally.

Another type of device for use in the delivery of medication makes useof an osmotic infusion pump. Generally the output from such an infusionpump is essentially constant and cannot be varied.

SUMMARY OF THE INVENTION

According to the invention there is provided a microfabricated devicewhich includes:

a structure defining a closed fluid delivery channel, the channel havingan inlet and an opposed outlet;

a conducting polymer actuator arranged within the fluid deliverychannel, at least a part of the actuator being configured to vary itscross sectional area in a direction transverse to a direction of fluidflow in the channel; and

an actuator control arrangement carried by the structure for controllingthe actuator to cause the actuator to expand and contract cyclically andsequentially along the length of the actuator to vary the crosssectional area of the channel cyclically and sequentially to effect aperistaltic pumping action to deliver fluid from the inlet of thechannel to the outlet of the channel.

By “closed fluid delivery channel” is meant that a part of the channelopposite the floor is covered by a cover member but the channel is openat its opposed ends.

The structure may include a base and a pair of spaced side wallsextending upwardly from the base, the side walls supporting a coverlayer spaced from the base to define the channel.

The structure may be formed by microfabrication techniques such asdeposition and etching techniques. Thus, for example, the structure maybe formed of silicon or any other suitably rigid material. A siliconstructure has the advantage that interfacing with other controlcircuitry is facilitated. Instead, the structure may comprise a glass orother inert substrate on which the actuator control arrangement isdeposited. The cover layer may be applied by micromachining techniques.

In one embodiment, the actuator may be arranged in the channel betweenthe side walls. Thus, an entire width of the actuator may be able tohave its cross sectional area varied. In another embodiment, theactuator may support the cover layer in a spaced position relative tothe base, a central part of the actuator being configured to vary itscross sectional area while side parts of the actuator are fixed andnon-varying and function as side walls to support the base and the covermember in spaced relationship.

The actuator may be a unitary, one-piece body or, instead, the actuatormay be made up of a plurality of discrete actuator elements arranged inseries in the channel. Where the actuator is a single body, adjacentparts of the body may be able to expand and contract independently ofeach other under the effect of the actuator control arrangement tocreate a peristaltic wave-like motion through the body from the inlet tothe outlet. In the case where the actuator comprises a series ofdiscrete actuator elements, the elements may be individually controlledby the actuator control arrangement to cause the peristaltic motionthrough the channel.

The actuator control arrangement may comprise an electrode arrayarrangement. The electrode array arrangement may comprise a plurality ofelectrode arrays to facilitate phased cyclic expansion and contractionof the actuator elements to effect the peristaltic pumping action.

At least three electrode arrays may be provided to provide a three phaseor higher phase actuation sequence to achieve directional flow of thefluid from the inlet of the fluid delivery channel to the outlet of thefluid delivery channel.

In the case where three electrode arrays are used, a counter electrodearrangement may be provided. A counter electrode may be associated witheach electrode array.

Instead, the electrode arrangement may comprise four electrode arraysarranged in two pairs. With this arrangement, one of the electrodearrays of each pair may be used as a counter electrode for the otherelectrode array of that pair.

The electrode array arrangement may be deposited on the structure by anappropriate deposition technique, for example, by sputtering, printing,or the like.

The conducting polymer actuator elements (or conjugated polymers) havethe capability to be reversibly oxidised and reduced upon theapplication of a potential difference. The conducting polymers of theactuator may be selected from the group consisting of polypyrrole andits derivatives, polyaniline and its derivatives, polythiophene and itsderivatives poly(ethylenedioxythiphene), polyphenylene,poly(pheylenevinylidene) and its derivatives, or the like.

It will be appreciated that, to effect expansion and contraction of theactuator elements, the actuator elements need to be immersed in anelectrolyte.

In one embodiment, a fluid to be pumped by the device is an electrolytewhich reduces and oxidises the actuator, the actuator being exposed tothe electrolyte in the channel. In another embodiment, a membrane mayseparate a fluid to be pumped through the device and an electrolyte inwhich the actuator is immersed. The membrane may be a thin polymermembrane made of materials such as siloxane-based polymers,polyvinylchloride film, polyvinylidene fluoride, polyethylene,polypropylene, or other non-permeable membrane. Further, the membranecould be of a silicone material.

The electrolyte may be one of a liquid electrolyte, a polymerelectrolyte, a polymer gel electrolyte and an ionic liquid.

The liquid electrolytes are aqueous and organic based solvents, such aspropylene carbonate, acetonitrile and gamma-butyrolactone. The liquidelectrolytes may contain supporting salts with either anion or cationsbeing able to move in and out of the conducting polymer material. Thesalts may be low molecular salts selected from the group consisting ofKCl, NaCl, KClO₄, tetrabutylammonium hexafluorophosphate,tetrabutylammonium triflouromethanesulfonate; surfactant type salts suchas sodium dodecylsulphonate; polyelectrolytes ionic liquids, such as1-butyl-3-methyl imidazolium tetrafluoroborate; or the like.

The polymer electrolytes and polymer gel electrolytes may be poly methylmethacrylate/lithium perchlorate in a propolyene carbonate/acetonitrilemixture as a solvent.

The actuator may be grown on the actuator control arrangement viaelectropolymerisation techniques or deposited on the substrate surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are now described by way of example withreference to the accompanying drawings in which:

FIG. 1 shows a schematic, side view of a microfabricated device, inaccordance with one embodiment of the invention;

FIG. 2 shows a schematic side view of a microfabricated device, inaccordance with another embodiment of the invention;

FIG. 3 shows a schematic end view of the device of FIG. 1;

FIG. 4 shows a schematic plan view of an actuator control arrangementfor the device of FIG. 1 or FIG. 2;

FIG. 5 shows a schematic side view of operation of the device of FIG. 1using the actuator control arrangement of FIG. 4;

FIG. 6 shows a schematic plan view of a further actuator controlarrangement;

FIGS. 7A and 7B show two sequences of operation of the actuators usingthe control arrangement of FIG. 6;

FIG. 8 shows a schematic, side view of a microfabricated device, inaccordance with another embodiment of the invention;

FIG. 9 shows a schematic, end view of a microfabricated device, inaccordance with yet a further embodiment of the invention;

FIG. 10A shows, above, a three dimensional AFM topographic image and,below, a cross-sectional line drawing end view of a first polypyrroleactuating element prepared for experimental purposes; and

FIG. 10B shows, above, a three dimensional AFM topographic image and,below, a cross-sectional line drawing end view of a second polypyrroleactuating element prepared for experimental purposes.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the drawings, reference numeral 10 generally designates amicrofabricated device, in accordance with an embodiment of theinvention. The device 10 includes a structure 12 defining a channel 14.The channel 14 has an inlet 16 and an opposed outlet 18. A plurality ofconducting polymer actuator elements, or actuators, 20 is arranged inthe channel 14 of the structure 12.

The device 10 includes an actuator control arrangement in the form of anelectrode array arrangement 22 for controlling operation of theactuators 20, as will be described in greater detail below. One exampleof an electrode array arrangement 22 is shown in FIG. 4 of the drawingswith another example of the electrode array arrangement 22 being shownin FIG. 6 of the drawings.

A particular application of the device 10 is as a micropump. Theinvention will be described with reference to that application belowalthough it will readily be appreciated by those skilled in the art thatthe invention could be used in other applications. The micropump 10 is aminiature device having dimensions in the micrometre scale.

The structure 12 comprises a substrate 24 having a pair of opposedsidewalls 26 defining the channel 14. A sealing, or cover, layer 28 ismounted on the walls 26 to define a closed fluid delivery channel 14 (asdefined).

The structure 12 is formed by any suitable microfabrication techniquessuch as, for example, deposition and etching techniques. Thus, thesubstrate 12 is a suitable material able to be deposited and etched suchas silicon or any other suitable rigid material that allows forelectrodeposition. An advantage of using silicon for the substrate 24 isits ability to interface electrically with other control circuitry.

The electrode array arrangement 22 can either be a three phasearrangement comprising three electrode arrays 30, 32 and 34 (FIG. 4) ora four electrode array arrangement comprising four electrode arrays 36,38, 40 and 42 (FIG. 6). Regardless of the configuration of the electrodearray arrangement 22, the electrode array arrangement 22 is deposited orotherwise applied to the substrate 24 in a suitable manner, for example,by sputtering, printing, or other suitable microfabrication techniques.It will be appreciated that the electrode arrays 30, 32 and 34 or 36-42are electrically insulated from each other so that each array controlsevery third or fourth actuator 20, as the case may be.

Thus, each electrode array 30-42 is a substantially comb-like structureand has a conductive strip 44 with a plurality of conductor pads, orelectrodes, 46 extending orthogonally from the conductive strip 44. Theconductor pads 46 are located on the base of the channel 14 and eachconductor pad 46 has an actuator 20 associated with it.

In the three phase arrangement 22 shown in FIG. 4 of the drawings, eachelectrode array 30, 32, 34 may have a counter electrode (not shown)associated with it. However, if the phases are controlled appropriately,i.e. by being 120° out of phase with one another, any two electrodes canact as the counter electrode for the third electrode obviating the needfor independent counter electrodes. In contrast, in the case of theelectrode arrays 36-42 as shown in FIG. 6 of the drawings, the electrodearrays 36-42 are arranged in pairs so that one electrode array of eachpair serves as a counter electrode for the other electrode array of thepair. Thus, because the electrode arrays 36 and 40 are 180° out of phasewith each other, they form an electrode array pair with the electrodearrays 36 and 40 forming counter electrodes for each other. Similarly,the electrode arrays 38 and 42 are arranged in a counter electrode pair.

The actuators 20 are conjugated polymer actuators, such as polypyrroleactuators, which are grown on the conducting pads or electrodes 46 ofthe electrode arrays by electropolymerisation.

Because the actuators 20 are conducting polymer actuators, they requirethe presence of an electrolyte for expansion and contraction, i.e.,oxidation and reduction. In the embodiment shown in FIG. 1 of thedrawings, it is assumed that the fluid to be pumped is the electrolyteand the actuators 20 are in direct contact with the fluid in the channel14. In the embodiment shown in FIG. 2 of the drawings, it is assumedthat the fluid to be pumped is not a suitable electrolyte. In that case,the channel 14 is separated into two zones, a pumping zone 14.1 and anactuator zone 14.2, by a membrane 48. The membrane 48 is of any suitablematerial such as a thin, polymer material. The polymer material is asiloxane-based polymer, polyvinylidene fluoride, polyethylene,polypropylene, or the like. The membrane 48 is applied via suitablemicrofabrication techniques, such as, for example, deposition andetching techniques.

The electrolyte is chosen from liquid electrolytes, polymerelectrolytes, polymer gel electrolytes and ionic liquids. The liquidelectrolytes are aqueous and organic solvent based. They containsupporting salts with either anions or cations being able to move in andout of the material of the polymer actuators 20. The salts are chosenfrom any suitable salt such as a low molecular salt, for example, KCl,KClO₄, TBAPF₆, TBACF₃SO₃, or the like; surfactant type salts, forexample dodecylbenzenesulphonate or alkyl sulphonates, polyelectrolytes,for example, polystyrenesulphonate or polyacrylic acid, and ionicliquids, for example, 1-butyl-3-methyl imidazolium tetrafluoroborate.

Polymer electrolytes and polymer gel electrolytes are selected fromsuitable polymer electrolytes such as poly(methyl methacrylate)/LiClO₄in propylene carbonate/acetonitrile mixture as a solvent.

The polymer of the actuators and the small size of the actuators 20,having a height in the order of 1 μm to a few μm's, is exploited toachieve high speed operation of the micropump 10 and high density ofactuators 20 on the substrate. Conducting polymers have largestrains/deformations in comparison with actuators in piezoelectricdevices. These large strains/deformations offer significant advantages.However, whilst polymer actuators with strains/deformations of more than20% are preferred, devices of the invention are still practical withlower strains/deformations, just requiring higher or deeper actuatingelements. The actuators 20 also have fast actuation, in the order of 1Hz. In addition, the channel 14 is designed to have a small fluidchannel cross-section relative to the width of the actuators 20 in orderto exploit hydraulic viscosity to improve hydrostatic pressures. Withthis configuration, the micropump 10 is able to operate without anyvalves.

The small channel 14 in combination with rapid actuation of theactuators 20 ensures that viscous effects of the fluid being pumpedassists in avoiding backflow of the pumped fluid even in the presence ofan adverse pressure gradient. The viscous effects of the fluid beingpumped cause a dynamic seal between the top of the actuators and thesealing layer 28 and around the sides of the actuators 20 and theinternal surfaces of the walls 36 of the structure 12 due to fluidfriction and inertia. In addition, a further consequence of the smallfluid channel 14 is the presence of a small dead volume with capillaryeffects being exploited to make the pump 10 self-priming.

Referring now to the electrode arrangement 22 shown in FIG. 4 and theactuators of FIG. 5, three separately controllable electrode arrays 30,32, 34 are provided so that every third actuator 20 moves in phase.Thus, as shown in FIG. 1 of the drawings, the actuators 20.1 move inphase with each other, the actuators 20.2 move in phase with each otherand the actuators 20.3 move in phase with each other. A similararrangement applies with respect to the embodiment of the micropump 10shown in FIG. 2 of the drawings where the actuators 20 act on themembrane 48. In both embodiments, appropriate control of the actuators20 in a cyclic and sequential manner causes a peristaltic pumping actionfrom the inlet 16 to the outlet 18 of the channel 14. Thus, byintroducing an appropriate phase delay (120° in the case of theelectrode array arrangement 22 of FIG. 4) between adjacent actuators20.1 and 20.2, 20.2 and 20.3 and 20.3 and 20.1, directional fluid motionin a direction of arrow 50 (FIG. 5) and a driving pressure gradient isachieved. In FIG. 5, actuator motion is shown by the arrows 52.

The pressure gradient can be increased by increasing the number ofgroups of actuators 20 (i.e. the number of units of 3 or 4 actuators)along the array arrangement 22 between the inlet 16 and the outlet 18.As a general rule, the total pressure difference will increase with anincreasing number of recurrent actuator groups used, all otherparameters being kept constant.

As previously indicated, with the electrode arrangement 22 of FIG. 4 ofthe drawings, any two electrodes may act as counter electrodes for thethird electrode providing that there is no phase error, or eachelectrode array 30, 32, 34 may have a counter electrode associated withit. Thus, as an actuator 20 is reduced or oxidised opposite chargemovement of equal magnitude occurs at a counter electrode.

Referring to the embodiment of the invention shown in FIGS. 6 and 7 ofthe drawings, with the provision of four electrode arrays 36-42 adjacentactuators 20 are always 90° out of phase with each other. Hence atravelling peristaltic “wave” motion can be generated as shown in thetwo sequences in FIG. 7 of the drawings. Once again, arrows 52 indicatedirection of actuator movement. Also, as previously described, with theelectrode arrangement of FIG. 6, the electrode array pairs serve ascounter electrodes for each other and the need for further counterelectrodes is obviated.

Referring now to FIG. 8 of the drawings, another embodiment of themicropump 10 is shown. With reference to the previous drawings, likereference numerals refer to like parts unless otherwise specified.

In this embodiment, the actuator is comprised of a single or unitarybody 60 arranged in the channel 14. The electrolyte is contained in thebody 60 or some external reservoir in communication with the body.Adjacent parts of the body are individually addressable by the electrodearray arrangement 22 to cause the parts of the body 60 to oxidise andreduce independently of each other as electrolyte is absorbed orexpelled, as the case may be. As a result, by appropriate control of thebody 60, a peristaltic wave-like motion is imparted to the body to drivefluid through the channel from the inlet 16 to the outlet 18.

In FIG. 9 of the drawings, yet a further embodiment of the micropump 10is illustrated. Once again, with reference to the previous drawings,like reference numerals refer to like parts unless otherwise specified.

The substrate 24 of the structure 12 and the cover layer 28 areseparated from each other by a conjugated polymer actuator 70 interposedbetween the substrate 24 and the cover layer 28. When viewed from theend, the actuator 70 has a central part 72 that is responsive toelectric fields generated by the electrode array arrangement 22. Incontrast, side parts 74 of the actuator 70 are not responsive to theelectric fields. The side parts 74 of the actuator 70 therefore serve asside walls to support the cover layer 28 in spaced relationship relativeto the substrate 24. When an electric field is applied to the actuator70 the central part 72 is reduced causing a channel 76 to open as shownin dotted lines. By cyclically and sequentially energising the centralpart 72 of the actuator 70, a peristaltic wave-like motion is generatedto cause fluid flow from the inlet 16 to the outlet 18 of the micropump10.

It will be appreciated that the actuator 70 could be implemented eitheras a single body, as described above with reference to the previousembodiment, or it could be implemented as a series of discrete actuatorssuch as the actuators 20 of the embodiment described with reference toFIGS. 1-7 of the drawings. Optionally, a membrane is interposed on thatsurface of the actuator 70 which is displaced, normally the surfacefacing an inner surface of the cover layer 28. The membrane serves toinhibit leakage of fluid through sides of the actuator 70. The membranemay be bonded to the surface of the actuator 70. The membrane, could bepreformed to form the channel 76 with the actuator 70 being activated tocompress the membrane to reduce the channel 76 to achieve theperistaltic pumping action.

Set out below are two examples of the preparation of polypyrrole (PPy)actuating elements suitable for use in the device 10.

EXAMPLE 1

FIG. 10A shows a polypyrrole (PPy) actuating element 80. In FIG. 10A,the upper illustration shows a three dimensional atomic force microscopy(AFM) topographic image of the polypyrrole (PPy) actuating element 80and the lower illustration shows a cross-sectional line drawing end viewof the polypyrrole (PPy) actuating element 80.

To form the element 80, polypyrrole (PPy) was depositedpotentiostatically at 0.85 V against Ag/AgCl on patterned parallel goldstrips (not shown) on a chip-like substrate on a 1.5 cm×1.5 cm glassplate (not shown) using a common connector for the working electrodes.The deposition solution was 0.1 M pyrrole and 0.1 M tetrabutylammoniumhexafluorophosphate (TBAPF₆) in propylene carbonate (PC). Theelectrochemical polymerization was stopped once the consumed chargereached 1 mC (for a working electrode area of 0.024 cm²), to obtain afilm thickness of about 2 μm. The PPy elements 80 were cycled inpyrrole-free solution of 0.1 M TBAPF₆ in propylene carbonate. Thealternative strips were then oxidized and reduced at a constantpotential of +1 V or −1 V for approximately 3 minutes. After theoxidation/reduction step, the chip was taken out of the electrolytesolution, patted briefly to remove the electrolyte solution from thesurface and measured by AFM (Nanoscope II). The section analysismeasurements were performed on at least 5 different positions.

When the PPy/PF₆ elements 80 were oxidized at +1V the oxidation causedan expansion of the film while reduction at the adjacent electrodecaused a shrinkage as illustrated in FIG. 10A. In FIG. 10A, a PPy strip82 to the left of a channel 84 was reduced at −1 V and a PPy strip 86 tothe right of the channel 84 was oxidized at +1 V. The difference in theheight of oxidized and reduced PPy elements was 66±4%. On oxidationpositive charges (polarons and bipolarons) were created on the polymerbackbone and PF₆ ⁻ anions and accompanying solvent entered the PPyelements 80 to balance the positive charges on the polymer and, as aresult, the polymer expanded considerably arising from the following:

PPy+PF₆ ⁻→PPy⁺.PF₆ ⁻+e

EXAMPLE 2

FIG. 10B shows a second polypyrrole (PPy) actuating element 80. Withreference to FIG. 10A, like reference numerals refer to like partsunless otherwise specified. Once again, in FIG. 10B, the upperillustration shows a three dimensional atomic force microscopy (AFM)topographic image of the polypyrrole (PPy) actuating element 80 and thelower illustration shows a cross-sectional line drawing end view of thepolypyrrole (PPy) actuating element 80.

The experiment was performed similarly to Example 1 above except thattetrabutylammonium triflouromethanesulfonate (TBACF₃SO₃) was used as anelectrolyte both for polymerisation and actuation. The AFM topographicimage shows that, in this case, the PPy strip 82 oxidized at +1V (to theleft of the channel 84) shrank and the PPy strip 86 reduced at −1 V (tothe right of the channel 84) expanded, which is opposite to Example 1.The section analysis showed that the average height change between 1.0 Vand −1.0 V was 47±10%.

The reduced state displayed a larger volume due to a cation insertionprocess caused by large CF₃SO₃ ⁻ anions being immobilized deep withinthe polymer structure during electropolymerisation. As the polymer isreduced and positive charges removed from the polymer, TBA⁺ cations andsolvent need to move in to the film to balance the negative charge ofthe residual CF₃SO₃ ⁻ ions as shown by the following:

PPy⁺.CF₃SO₃ ⁻+TBA⁺+e⁻→PPyTBACF₃SO₃

This results in film swelling.

Examples 1 and 2 demonstrate that both anion and cation movement can beused for the actuation of PPy actuating elements depending on the choiceof electrolyte used during the polymer synthesis and actuation.

Hence, by means of the invention, a micropump 10 is provided which canbe accurately controlled electrically, has actuators 20 which exhibitlarge strains, i.e. deformation of the actuators 20, and requires lowvoltage to operate, the applied voltage being of the order of about 1volt. As a result, the micropump 10 can be manufactured from very smallcomponents and the dielectric strength of the material need not beselected to withstand high voltages. In addition, the micropump 10 canbe made from or encapsulated in biocompatible materials for implantationin the human body to be used for controlled released drug delivery orrelated applications. The micropump 10 can also be used in microfluidicapplications and “lab-on-a-chip” applications. Still further, themicropump 10 can be used in analytic devices and portable desalinationsystems.

It is an advantage of the invention that a micropump 10 is providedwhich, being of all solid-state fabrication, can be manufactured bymicromachining techniques, including, for example, photolithography. Itis of compact dimensions and lightweight. Further, as indicated above,the micropump 10 can be of a biocompatible material or encapsulated in abiocompatible material for implantation purposes. Due to the fact thatnon-metallic components are used, the need for biocompatible metalliccomponents, such as titanium components, is obviated. In addition, themicropump 10 has no mechanically moving parts and, as a result, shouldbe able to operate over long periods of time. Related to this is thefact that no valves are required thereby further improving the wearresistance of the micropump 10. The micropump 10 can also be used in abi-directional manner by appropriate actuation of the actuators 20.

The micropump 10 is a small volume device enabling metering of fluids inthe picolitre, nanolitre and microlitre ranges and is able to beimplanted into patients for controlled released drug delivery.

The use of conducting polymers as actuators enables largestrains/deformations at low voltages in comparison with piezoelectricdevices, which carries the benefit of reducing the overall height of thedevice. Further, the use of polymers simplifies manufacture and resultsin a relatively inexpensive, disposable device which is also lessfragile than existing micropumps.

The use of a silicon substrate 24 for the structure 12 renders themicropump 10 suitable for interconnection with control circuitry toenable the micropump 10 to be controlled, possibly externally of thepatient's body, by suitable wireless interfaces. The micropump 10 canalso be integrated with a microprocessor to provide refined control ofdrug delivery. Hence dosages can be altered externally of the patient'sbody by means of the processor and the wireless interface.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A microfabricated device which includes: a structure defining aclosed fluid delivery channel, the channel having an inlet and anopposed outlet; a conducting polymer actuator arranged within the fluiddelivery channel, at least a part of the actuator being configured tovary its cross sectional area in a direction transverse to a directionof fluid flow in the channel; and an actuator control arrangementcarried by the structure for controlling the actuator to cause theactuator to expand and contract cyclically and sequentially along thelength of the actuator to vary the cross sectional area of the channelcyclically and sequentially to effect a peristaltic pumping action todeliver fluid from the inlet of the channel to the outlet of thechannel.
 2. The device of claim 1 in which the structure includes a baseand a pair of spaced side walls extending upwardly from the base, theside walls supporting a cover layer spaced from the base to define thechannel.
 3. The device of claim 2 in which the cover layer is applied bymicromachining techniques.
 4. The device of claim 2 in which theactuator is arranged in the channel between the side walls.
 5. Thedevice of claim 2 in which the actuator supports the cover layer in aspaced position relative to the base, a central part of the actuatorbeing configured to vary its cross sectional area while side parts ofthe actuator function as side walls to support the base and the covermember in spaced relationship.
 6. The device of claim 1 in which theactuator is a unitary, one-piece body.
 7. The device of claim 1 in whichthe actuator is made up of a plurality of discrete actuator elementsarranged in series in the channel.
 8. The device of claim 1 in which theactuator control arrangement comprises an electrode array arrangement.9. The device of claim 8 in which the electrode array arrangementcomprises a plurality of electrode arrays to facilitate phased cyclicexpansion and contraction of the actuator elements to effect theperistaltic pumping action.
 10. The device of claim 8 in which theelectrode array arrangement is deposited on the structure by adeposition technique
 11. The device of claim 1 in which conductingpolymers of the actuator are selected from the group consisting ofpolypyrrole and its derivatives, polyaniline and its derivatives,polythiophene and its derivatives poly(ethylenedioxythiphene),polyphenylene, poly(pheylenevinylidene) and its derivatives.
 12. Thedevice of claim 1 in which a fluid to be pumped by the device is anelectrolyte which reduces and oxidises the actuator, the actuator beingexposed to the electrolyte in the channel.
 13. The device of claim 1 inwhich a membrane separates a fluid to be pumped through the device andan electrolyte in which the actuator is immersed.
 14. The device ofclaim 13 in which the membrane is a polymer membrane.
 15. The device ofclaim 12 in which the electrolyte is one of a liquid electrolyte, apolymer electrolyte, a polymer gel electrolyte and an ionic liquid. 16.The device of claim 15 in which the liquid electrolytes are aqueous andorganic based solvents.
 17. The device of claim 16 in which the liquidelectrolytes contain supporting salts with either anion or cations beingable to move in and out of the conducting polymer material.
 18. Thedevice of claim 17 in which the salts are low molecular salts selectedfrom the group consisting of KCl, NaCl, KClO₄, tetrabutylammoniumhexafluorophosphate, tetrabutylammonium triflouromethanesulfonate. 19.The device of claim 17 in which the salts are surfactant type salts. 20.The device of claim 17 in which the salts are polyelectrolyte ionicliquids.
 21. The device of claim 15 in which the polymer electrolytesand polymer gel electrolytes are poly methyl methacrylate/lithiumperchlorate in a propolyene carbonate/acetonitrile mixture as a solvent.22. The device of claim 1 in which the actuator is grown on the actuatorcontrol arrangement via electropolymerisation techniques or deposited onthe substrate surface.